Plans to Optimise Distributed Grid of the Future

Plans to Optimise Distributed Grid of the Future

For years now, utility San Diego Gas & Electric (SDG&E) has been planning a multi-million-dollar investment in technology to help it monitor and manage the solar panels, plug-in electric vehicles, energy storage assets and demand response capabilities on the customer side of its grid.

SDG&E calls it a distributed energy resources management system, or DERMS. According to the utilitys 2011 smart grid deployment plan, the system should be fully functional and interfacing with customer loads and resources, supporting the planning and utilisation of all distributed energy resources in the utilitys service territory.

Tying together smart meters, solar inverters, smart thermostats, building management systems, behind-the-meter batteries and other new devices on a distribution grid never designed to manage all that complexity is a huge order. Its also more or less the set of changes that California regulators are demanding the state's three big investor-owned utilities -- SDG&E, Southern California Edison and Pacific Gas & Electric -- take on over the coming years.

Now, SDG&E is finally getting underway with its DERMS project, and has picked the first site for testing it out, said Tom Bialek, chief engineer with the utilitys smart grid team, in a recent interview.

SDG&E has also named a contractor to provide the distributed grid control technology, he said -- Colorado-based Spirae. A Spirae spokesperson declined to comment on the company's partnership with SDG&E, but the company is a veteran of microgrid projects in Colorado, Denmark and, notably, in San Diego, where it has worked on projects with the University of California at San Diego and the U.S. Navy. SDG&E and Spirae also shared the Department of Energy as a funder of separate Renewable Distributed Systems Integration projects, Bialek said.

Spirae won the contract after a nearly year-long competition with about twenty bidding vendors, on the basis of a whole pile of requirements for a DERMS project, he said. According to SDG&Es public descriptions of its DERMS plan, those include:

Dispatching energy assets on both the supply and demand sides of the distributed fleet. For example, it could direct home area network devices to ask thermostats to ease up on the air conditioning, or EVs to slow or stop charging, or batteries to discharge back to the grid; Forecast these supply-demand conditions up to 24 to 48 hours in advance; Integrate with SDG&Es smart meter, outage management and distribution management systems, to trade data about grid stresses and solutions back and forth; Communicating outside the utility. According to a 2010 SG&E presentation, the DERMS system should connect with company and third-party systems and services (e.g., virtual load groups, demand response aggregators) to optimize both company-operated and third-party operated resources and demand.

A federated, distributed, hierarchical structure for the grid edge

So how are SDG&E and Spirae putting this puzzle together? Bialek described the plan as a federated, distributed, hierarchical structure, which overlays existing distribution grid SCADA and wireless networks, but interacts with them at a local and system-wide level.

The structure is federated because it deploys DERMS alongside SDG&Es existing network management system, which runs on SCADA and is operated by Oracle's NMS platform. You can look at the distribution management system (DMS) as the interface which the operations folks use to conduct day-to-day business," he said. "The DERMS is whats looking for whats out there and how I can optimise it.

Its both distributed and hierarchical because Spiraes grid-hardened router-sensor-controller devices will be deployed in SDG&Es grid, where they will act both as servants of the grid operator and agents of control for local grid conditions.

They have various levels of controllers, including the asset management controller. which allows some autonomous function, but reports up to a higher level area controller, he said. That area controller reports in turn to the grid operator along the DMS, which remains in control of big grid decisions.

Meanwhile, the DERMS platform will be running these optimisation algorithms to [figure out], If I ran this instead, I could get this other result, he said. Then it would ask for permission from the DMS: I can do this; do you want me to do this?

Some of the goals of this bilateral grid optimisation structure include balancing energy supply and demand at a local level, perhaps by balancing solar power fluctuations with batteries or smart home energy controllers. Distributed solar power can also cause local voltage and power factor disturbances that need to be managed.

To help mitigate the problems, the DERMS platform could request permission to island a portion of the local grid, adjust the amount of solar energy being stored in batteries from moment to moment, ask customers to ease off on their air conditioning, or any combination of the above.

Part of the longer term vision for this particular product will be able to talk to and control lots of distributed energy devices, in general, said Bialek.

Desert microgrids, self-sustaining solar-storage communities

Borrego Springs, California, an inland desert town of 2,780 power customers, four golf courses and no stoplights served by one transmission line, is the first test site for the DERMS project, Bialek said.

Since 2009, SDG&Es DOE-funded microgrid project in Borrego Springs has hosted a network of rooftop solar, substation batteries, backup diesel generators and intelligent grid switches into a self-powering island, one that was able to keep the town's most vital infrastructure running during a 2013 outage.

Now were expanding the Borrego project, calling it Borrego 2.0, he said. Were trying to island the entire community with solar, using the energy storage thats out there, and dropping down to critical loads at night, and being able to island as long as we need to, only running the diesel generators as a last resort.

SDG&E hasn't chosen its next sites for its DERMS deployment, but Bialek noted several other projects the utility has underway that could be suitable targets. One is the Civita master-planned development, where a community center are being hooked up with solar, batteries, fuel cells and home energy management devices. One of the first use cases could be smoothly disconnecting the community center from the grid during emergencies, using on-site generation and storage along with some waste heat management, he said. Since its a multi-stage housing development, as the phasing expands, well expand the functionality that well implement, he said.

SDG&E is installing batteries at Civita and Borrego Springs as part of a broader distributed energy storage plan, and has 6 megawatts of substation-connected batteries and nearly 5 megawatts of customer-owned storage connected to date, making battery management an important facet of its DERMS work, he said. So are electric vehicles -- last month, SDG&E filed a proposal for an EV-to-grid integration project that's seeking $100 million to install up to 5,500 charging stations in groups of ten or more per site, focused on giving people a place to recharge while theyre at work.